Page 222 - Canadian BC Science 9

6.2 Sexual Reproduction
In sexual reproduction, a male gamete (sperm cell) must fertilize a female gamete (egg cell). As a result of meiosis and the union of sperm and egg cells, no two individuals will have the same DNA, except identical twins. Many aquatic animals reproduce through external fertilization. Most land animals reproduce through internal fertilization. Following fertilization, the zygote and embryo start to divide by mitosis, and cells will differentiate.
Words to Know
differentiation embryonic development external fertilization internal fertilization mating
204 MHR • Unit 2 Reproduction
Figure 6.14
The purple sea urchin has been used extensively in scientific research.
Purple sea urchins are familiar sights along the coast of British Columbia (Figure 6.14) and are one of the most useful models for scientific research. In fact, the sexual reproductive process of the sea urchin has been studied for decades, enabling scientists to gain a greater understanding of how animal sperm cells and animal egg cells meet and result in fertilization.
In Chapter 5, you learned that asexual reproduction requires only one parent and can occur wherever that parent is located if conditions are favourable. Sexual reproduction requires two parents who must bring two gametes together for fertilization to occur. To survive, sexually reproducing species must mate with members of their own species. For years, scientists wondered how different types of sea urchins living close together were able to accomplish sexual reproduction within their own species, since sea urchins bring gametes together by releasing great clouds of sperm and egg cells into the water.